Im using as2.0 to try and build a slider to control the alpha of another movie clip

1

hi
i was wondering if u could help me, iam trying to bulid a slider which will change the alpha of another movie clip named light.
how do i do this.
here is the actionscript i have so far:

onClipEvent (load) {
	top = _y;
	bottom = _y;
	left = _x;
	right = _x+100;
}

this actionscript is on a movie clip containing the slider button, and on the button is the actionscript bellow:

on (press) {
    startDrag("", false, left, top, right, bottom);
}
on (release) {
    stopDrag();
}

Thanx for any help